Polyblastus stenocentrus
Holmgren, 1857
Polyblastus stenocentrus is a small ichneumon in the tribe Tryphonini. It is a of , with females carrying unusually large loads compared to related wasps. The has been documented in Colorado and Alberta, Canada. Observations suggest females may carry egg clusters externally on the , a whose function remains incompletely understood.
Pronunciation
How to pronounce Polyblastus stenocentrus: //pɔliˈblastəs stɛnoʊˈsɛntrəs//
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Identification
Identification to from images alone is considered exceptional; most ichneumon require examination of morphological characters for reliable determination beyond . Small body size and placement in tribe Tryphonini are distinguishing features at higher taxonomic levels.
Distribution
Documented from Fountain, Colorado, USA and Edmonton, Alberta, Canada. The likely occurs more broadly in North America where suitable are present.
Seasonality
have been observed in early June in Colorado.
Host Associations
- Cimbex americana - Elm , a potential ; observed at same location and date as P. stenocentrus in Colorado
Life Cycle
: feeds externally on larva , which continues development until larva completes its growth. wasp emerges from spun by the host sawfly larva.
Behavior
Females have been observed carrying clusters of on the underside of the . This may result from accumulation of eggs remaining on the after unsuccessful attempts, though the adaptive significance of carrying multiple eggs externally is unclear.
Ecological Role
of ; contributes to of sawflies, which are herbivorous .
Similar Taxa
- Idiobiont ichneumon waspsP. stenocentrus differs in : arrest development at time of and typically have smaller loads; P. stenocentrus is a allowing continued host development and carries significantly larger egg loads
More Details
Egg load characteristics
According to Cummins et al. (2011), Ctenoplematinae including Polyblastus have significantly larger loads than , though their individual eggs are smaller. This represents a life- trade-off associated with strategy.
Taxonomic identification note
The identification of this specimen to from photographs was noted as surprising by observers, given that most ichneumon cannot be reliably identified beyond from images alone.